Safe failure measuring and controlling apparatus



Dec. 28, 1948. R. F. WILD 2,457,791

SAFE FAILURE MEASURING AND CONTROLLING APPARATUS Filed June 21, 1946 k 8Sheets-Sheet 1 INVENTOR. RUDOLF F. WILD ATTORNEY.

R. F. WILD Dec. 28, 1948.

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R. F. WILD Dec. 28, 1948.

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INVENTOR. RUDOLF F. WILD ATTORNEY.

R. F. WILD Dec. 28, 1948.

SAFE FAILURE MEASURING AND CONTROLLING APPARATUS 8 Sheets-Sheet 6 FiledJune 21, 1946 IN VEN TOR.

RUDOLF F. WILD BY W ATTORNEY.

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SAFE FAILURE MEASURING AND CONTROLLING APPARATUS 8 Sheets-Sheet 7 FiledJune 21, 1946 mmvmx. RUDOLF F. WILD ATTORNEY.

Dec. 28, 1948. R. F. WILD 2,457,791

SAFE FAILURE MEASURING AND CONTROLLING APPARATUS Filed June 21, 1946 sSheets-Sheet 8 INVENTOR. RUDOLF E WILD ATTORNEY.

Patented Dec. 28, 1948 SAFE FAILURE MEASURING AND CONTROLLING APPARATUSRudolf F. Wild, Philadelphia, Pa assignor to The Brown InstrumentCompany, Philadelphia, Pa., a corporation of Pennsylvania ApplicationJune 21, 1946, Serial No. 678,255

13 Claims. 1

The present invention relates to measuring and control apparatus of thetype comprising electronic amplifying means through which variations ina minute voltage being measured control the operation ofmechanismemployed to effect operations on and in accordance withvariations in said voltage. Such apparatus may be of widely divergentforms. For example, it may comprise an integrator actuated through anelectronic amplifier by a millivoltmeter, or it may be a selfbalancingpotentiometer including an electronically controlled rebalancing motor.

The general object of the invention is to provide improved means fordetecting the inability of the apparatus of the above-mentioned type tofunction properly as a result of any one of a variety of apparatusdefects. In a desirable form of embodiment in self-balancingpotentiometric measuring and control apparatus, the invention is used todetect the operative failure of the potentiometric measuring circuit, ofthe thermocouple connected to said circuit, of any one of the inputvoltage and power transformers, of the electronic amplifying valves, orof the rebalancing motor itself. In another form of embodiment in suchmeasuring and control apparatus, the present invention is used not onlyto detect the operative failure of various components of the apparatus,but also to effect replacement of the defective components with suitablestand-by components. This embodiment is of particular utility inconnection with controlled processes where it is highly desirable tomaintain automatic control of the process at all times, and where it isundesirable to interrupt automatic control upon failure of one or morecomponents of the controlling apparatus. The degree of the importance ofmaintaining automatic process control upon apparatus failure determinesthe extent to which stand-by equipment should be provided.

My invention is characterized by the utilization of the amplifyingsystem of the apparatus in creating a high frequency, oscillatingcurrent which is used to indicate the occurrence of an apparatusfailure, which may be used to control a stand-by system, and which isordinarily used for the "safe failure purpose of producing a controleffect to minimize the injurious consequences of the apparatus failure.In the embodiment of the invention mentioned above a high frequencycurrent flow is maintained while the potentiometer is in normaloperation, and is interrupted when the potentiometer ceases to benormally operative, and the interruption results in actuating a signaland in interrupting the operation of the rebalancing motor. Ifdesirable, the control efiect resulting from apparatus failure may bemade to cause a shut-down of the controlled process by shutting off thesupply of fuel to a furnace, for example. However, in certain processes,particularly those of the oil refining industry, it is not desirable toshut-down the operation of the system upon failure of the controlapparatus Instead, it is desirable to provide either visible or audibleindication, or both, upon such control apparatus failure, and to deprivethe faulty apparatus of control of the process so that an operator cantake over manual control of the process and manually maintain it inoperation, thereby avoiding the waste of time and materials which occursif such a process is shut down before its completion. Also, if desirableand practically necessary, suitable standby apparatus may be providedwhich will automatically be connected to the system to replacecomponents which have failed.

The present invention is further characterized by the relatively few andsimple changes and additions required for the use of the presentinvention in self-balancing potentiometers including electronicamplifying apparatus of a conversion type now in extensive use.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a. better understanding of theinvention, however, its advantages, and specific objects attained by itsuse, reference should be had to the accompanying drawings anddescriptive matter in which I have illustrated and described preferredembodiments of the invention.

Of the drawings:

Fig. 1 is a diagrammatic representation of potentiometric apparatusincluding my improved means for producing a control action on thefailure of various apparatus elements;

Fig. 2 is a simplified diagram illustrating characteristic features ofthe arrangement shown in Fig. 1;

Fig. 3 is a diagram illustrating a modification of the oscillationdetecting circuit portion of the apparatus shown in Fig. 1;

Fig. 4 is a diagram illustrating the use of the present invention inproviding automatic standby protection;

Fig. 5 is a diagram of a modification of the ap- Fig. 5A is adiagrammatic representation of a portion of the apparatus oi. Fig. 5;

Fig. 6 is a diagram oi. another modification oi the apparatus oi Fig. 4wherein additional standby apparatus is provided;

Fig. 7 is the diagram 01 a modification of the apparatus of Fig. 8adapted iorcontrol purposes;

Fig. 8 is a diagram illustrating the adaptation of the present inventionto a system employing a diflerent standardizing circuit from that o! thesystem of Fig. l; and

Figs. 9, i0, and 11 illustrate in detail portions of the apparatus oiFig. 8.

In Fig. 1, I have diagrammatically illustrated the use of the presentinvention in potentiometric measuring and control apparatus oi thesocalled conversion type disclosed in the prior application of Walter P.Wills, Serial No. 421,173, filed December 1, 1941, now matured intoPatent No. 2,423,540 issued July 8, 1947. In the apparatus shown, thepotentiometric rebaiancing operations are eflected by a reversibleelectric motor J, and an automatic cont ol system which controls theoperation of thdnotor J, and includes an electronic amplifier and meanscomprising a, pulsator I, and a transformer H cooperating to impress onthe electronic amplifier an alternating control voltage varying inmagnitude and phase with the magnitude and direction or potentiometricbridge unbalance, produced by variations in the output of thethermocouple E which is the source oi a small D. C. voltage.

The apparatus shown diagrammatically in Fig. 1 comprises apotentiometric bridge circuit A including a slide wire resistance Balong which a slider contact C is adjusted through a' shaft J which isrotated by the motor J, and is in threaded engagement with the pencarriage D carrying the contact C. The tentiometric bridge circuit A isshown as of conventional type comprising one branch including seriesconnected resistances I, 2 and I, an energizing branch connected inparallel with the first mentioned branch and including a source orcurrent 4 and a regulable resistance 5 connected in series, and athird.,

branch connected in parallel with the energizing branch and with thefirst mentioned branch and including series connected resistances 5and 1. The slide wire resistance B is connected in parallel with theresistance I between and in series with the resistances 2 and 3.

Associated with the bridge circuit A is a standardizing switch. Thelatter, as conventionally shown, comprises a movable two-position switchmember G and switch contacts G, G and G. In the normal operatingposition of the switch member G, it engages the contact G and connectsthe thermocouple E between the slider contact C and the Junction point Fof the bridge resistances 6 and I. In its recalibrating position, theswitch member G engages and forms a bridge connection between thecontacts G and G and thereby connects a resistance 8 and a standard cell9 in series with the bridge resistance 1. In respect to its featuresjust specifically mentioned, the apparatus shown diagrammatically inFig. 1 does not difler significantly from the apparatus shown in saidprior Wills application.

As shown, the circuit branch connecting slider contact C and bridgepoint F includes in series between the contact C and switch contact G,the thermocouple E, conductor 20, resistances 2i and 22, the secondarywinding 23 of a transformer 24, and a conductor 25. The circuit elements22,

1i and 23 are shunted by a condenser 26. The

transformer 24 couples the input and output circuits of the electronicamplifying. and control system shortly to be described. The transformer24 has an iron core 28 which may be adjusted to vary the magnitude ofthe feed-back, or regenerative effect transmitted to said input circult.The primary winding 30 of transformer 24 has one terminal connected byconductor 58 to one terminal 59' of the control winding Si 01 the motorJ. The second terminal of the primary winding 30 is connected to groundon the closure of a starting switch 3|. When, after the apparatus isthus started into normal operation the starting switch is opened, theground connection to the winding 30 is maintained by a relay switch I I5associated with the high frequency current detection circuitshown inFig. 1 and hereinafter described. A condenser 32 is connected inparallel with the primary winding 30. The terminal of the thermocouple Econnected to the resistance 22 is directly connected to the bridge pointF by a condenser 33.

The circuit connection between the switch contact G and the bridge pointF closed by the movement of the switch member G into engagement with thecontact G, includes a conductor connecting the switch member G to themidpoint of the two sections 4i and 42 c! the primary winding of thetransformer H. A condenser 39 connects the conductors 4|! and 25 for apurpose hereinafter explained. The core structure and casing of thetransformer H and a shield 43 interposed between the transformer primarywindings and its secondary winding 4 are connected to a groundingconductor 45. The latter is also connected to the junction point of theprimary winding sections ll and 42. The remote ends or terminals of theprimary winding sections 4| and 42 are connected to the stationarycontacts 46 and I! respectively of the vibrator I. The latter comprisesa vibrating reed 48 carrying a contact moved by the vibration of thereed back and forth between the contacts and 41 which it alternatelyengages.

The vibrating contact 48 is connected by conductor 48' to the bridgepoint F. The reed I8 is caused to vibrate by a winding 49 having itsterminals connected to a source of alternating current. A permanentmagnet 49', connected to ground, is associated with the reed 48 forpolarizing and synchronizing purposes, and in operation the reed 48 isin continuous vibration with a irequency corresponding to that of thesource of energization for the winding 49. In consequence,

- the currents flowing alternately through the winding sections Al and42 create alternating voltages in the secondary winding 44 well adaptedfor amplification in the electronic relay to the input terminals oi.which the terminals of the transformer secondary winding 44 areconnected.

Said electronic relay comprises a drive section and an amplifyingsection, both of which receive energizing current from a transformer Ihaving its primary winding 50 connected to the supply conductors L andIF and having three secondary winding sections 5|, 52, and 53. The drivesection of the electronic relay comprises the reversibly rotating motorJ and an electronic tube K. The amplifying section comprises amplifyingtubes L and M.

The motor J, as diagrammatically shown, comprises a rotor 54mechanically coupled to the threaded shalt J, the rotation of which, asdiagrammatically shown, simultaneously adjusts the contact C'and the,pen carriage D. The motor J has a pair of terminals 55 and 58 connectedthrough a condenser 51 of suitable value to the alternating supplyconductors L and L, and has a second pair of terminals 58 and 59'. Theterminal 58 is connected to the midpoint 98 of the secondary winding i,and terminal 59' is connected to ground through the conductor 59 and theprimary winding 30 of the transformer 24 when either of switches 3| andI I6 is closed. For its intended use, the motor J may be of the formschematically shown in the drawings in which one pair of oppositelydisposed field poles is surrounded by a winding 50 connected between themotor terminals 55 and 56, and the other pair of poles is surrounded bya winding 6| connected between the motor terminals 58 and 59'.

Since the value of the condenser 51 is so chosen as to produce with thewinding 60 a series resonant circuit, the current flowing through themotor winding 60 will be approximately in phase with the voltage of thealternating supply conductors L and L The current supply to the winding6| will either lead or lag the voltage of the alternating current supplyconductors L' and L by approximately 90. The windings 60 and 6! thusestablish fields in the motor J which are displaced from one anotherapproximately 90 in one direction or the other, depending upon whetherthe winding 6| is energized with current which leads or lags the voltageof the alternating supply conductors L and L As will become apparentfrom the subsequent description, the phase of the current flow throughthe winding ill and the rotation of the rotor 54 depends upon, and iscontrolled by, the direction of unbalance of the potentiometricmeasuring circuit, and the duration of said rotation depends on theduration of said unbalance so that the rotation of the rotor 54 tends toadjust the contact C to the extent as well as in the direction torebalance said circuit.

The alternating voltage generated in the secondary winding 44 of thetransformer H is amplified through the action of the amplifying tubes Land M and the amplification thus effected is utilized in energizing thephase winding 6] of the motor J to control the selective actuation ofthe latter for rotation of the rotor 54 in one direction or the other.

As shown, the electronic amplifying tube L includes two heater typetriodes within the same envelope and designated by the reference symbols63 and 64. The triode 63 includes anode, control electrode, cathode, andheater filament elements, and the triode 64 includes like elements. Thefilaments of the triodes 53 and 64 are connected in parallel and receiveenergizing current from the low voltage secondary winding 53 of thetransformer I. The conductors through which the secondary 53 suppliescurrent to the heater filaments of the electronic tube L and also to theheater filaments of the tubes M, K, I00, and I01 have not been shown in,order not to confuse the drawings.

The electronic amplifying tube M'includes two heater type triodes,designated by the reference characters 55 and 66, and within the sameenveope. Both of the triodes of tube M includeanode, control electrode,cathode and heater filament elements. The electronic tube K alsoincludes two heater type triodes, which have been designated by thereference characters 61 and 68, within the same envelope. and whichinclude anode, control electrode, cathode, and heater filament elements.

The triode 88 of the electronic valve M is utilized as a half-waverectifier to provide a source of direct current voltage for energizingthe anode or output circuits of the triodes 63, 64 and 65. As shown, thecontrol electrode and cathode of the triode 66 are directly connected toeach other, and the output circuit thereof is energized by thetransformer secondary winding 52 through a circuit which may be tracedfrom the left end terminal of the winding 52, as seen in the drawings,through the conductor 69 to the anode of the triode '66, the cathodethereof, and through a conductor 10 to the positive input terminal 15 ofa filter generally designated by the reference numeral II. The negativeterminal 14 of filter II is connected by a conductor 12 to the right endterminal of the transformer secondary winding 52, which in turn isconnected through the conductor 85 to the grounded conductor 45.

The filter ll includes a condenser 13 which operates to smooth out theripple in the output voltage of the filter between the points 14 and 15.The filter "II also includes a resistance 16 and a condenser 11 whichoperate to smooth out the output voltage of the filter between thepoints I4 and 18. The filter 1| includes a further resistance l9 and acondenser 80 for smoothing out the output voltage between the filterpoints 14 and 8 l. The filter, therefore, comprises three stages. Such athree-stage filter is provided because for satisfactory and eflicientoperation it is desirable that the anode voltage supplied to the triode63 i be substantially free from ripple whereas it is not necessary tosupply anode voltage so completely free-from ripple to the outputcircuit of the triode ,64. Likewise it is not necessary to supply anodevoltage as free from ripple to the triode 65 as to the triode 64.

The anode circuit of the triode 63 may be traced from the filter pointBI, which comprises the positive output terminal of the filter, througha fixed resistance 82 to the anode of the triode 63, to the cathodethereof, and through a cathode biasing resistance 83, which is shuntedby a condenser 84, to the negative filter point 14 through thepreviously mentioned grounded conductor 45, the conductor and theconductor 12. The cathode biasing resistance 83 and the parallelconnected condenser 84 are utilized for biasing the control electrode ofthe triode 63 negatively with respect to its associated cathode.

The input circuit of the triode 63 may be traced from the cathode to theparallel connected resistance 83 and condenser 84, through thetransformer secondary winding 44, and through a conductor 86 to thecontrol electrode of the triode 63.

The output circuit of the triode 63 is resistancecapacity coupled to theinput circuit of the triode by means of a condenser 81 and a resistance88. More particularly, the anode of the triode 63 is connected bycondenser 81 to the control electrode of the triode 64, and the controlelectrode of the triode 64 is connected through t e resistance 88 to thegrounded conductor 45 and thereby to the grounded cathode of the triode64. The anode circuit of the triode 64 may be traced from the positiveterminal 18 of the fi ter H through a fixed resistance 89 to the anodeof the triode 64, the cathode thereof, and conductors 45. 85, and 12 tothe negative terminal 14 of the filter.

The output circuit of the triode 64 is resistancecapacity coupled to theinput circuit of the triode 85 by means of a condenser 90 which isconnected between the anode of the triode 64 and the control electrodeof the triode 55, and by means of a resistance 9| which is connectedbetween the control electrode of the triode 55 and the grounded cathodethereof. It is noted that the resistances 95 and 9| which are connectedto the input circuits of the triodes 64 and 95, respectively, operate tomaintain the control electrodes of the triodes 54 and 65 at the samepotentials as their associated cathodes when no voltage is induced inthe transformer secondary winding 44, but upon the induction of analternating voltage in the secondary winding 44, resistances 88 and 8|permit the flow of grid current between the control electrodes of thetriodes 64 and 65 and their associated cathodes and thereby limit theextent to which the control electrodes of these triodes are permitted togo positive with respect to their associated cathodes. With the controlelectrode of triode 65 connected to the resistance 9| by an adjustablecontactor 9|, as shown, said resistance 1.

and contactor form a means for varying the amount of signal impressed onthe control electrode of the triode 65 from the plate circuit of thetriode 64.

The anode circuit of the triode 65 may be traced from the positiveterminal 15 of the filter ll through a fixed resistance 92 to the anodeof the triode 65, the cathode thereof, and conductors 85 and 12 to thenegative terminal 14 of the filter. The output circuit of the triode 85is resistancecapacity coupled to the input circuits of the triodes 81and 69 by means including a condenser 93 and a resistance 94.

As illustrated the condenser 93 is connected between the anode of thetriode B and a conductor 95, which in turn is connected to the controlelectrodes of the triodes 61 and 68, and the conductor 95 is alsoconnected to the cathodes of those triodes through-the resistances 94and 91. Specifically, the resistance 94 is connected between theconductor 95 and ground, the resistance 91 is connected between thecathodes of the triodes 51 and 69 and ground. The resistance 94 limitsthe extent to which the control electrodes of the triodes 61 and 68 maybe driven positive with respect to their associated cathodes.

A voltage is supplied the output circuit of the triodes 61 and 58 fromthe high voltage secondary winding 5| of the transformer I. The anode ofthe triode 61 is connected to the left end terminal of the transformersecondary winding 5| and the anode of the triode 68 is connected to theright end terminal of the transformer secondary winding 5i. The cathodesof the triodes 61 and 69 are connected together and through the fixedresistance 91 to ground, and the terminal 59' of the motor J is alsoconnected to the ground through the transformer winding 90 and theswitches 3| and H6 as previously explained. The terminal 59 of the motorJ is connected to the center tap 98 on the transformer secondary winding5|. Thus, the triodes 61 and 69 are utilized for supplying energizingcurrent from the transformer secondary winding 5| to the phase windiniii of motor J.

The motor J is preferably so constructed that the impedance of thewinding BI is of the proper value to match the impedance of the anodecircults of the triodes 61 and 69 when the motor is operating in orderto obtain the most eillcient -7 during the running condition of themotor with the least amount of heating, and also provides a lowimpedance path for braking purposes.

As noted hereinbefore, energizing current is supplied to the motorwinding 6|] from the alternating current supply conductors L and Lthrough the condenser 51. As previously explained, the condenser 51 isso selected with respect to the inductance of the motor winding Gil asto provide a series resonant circuit havin a unity power factor. Byvirtue of the series resonant circuit, the total impedance of the motorwinding 60 is substantially equal to the resistance 'of the winding, andsince this resistance is relatively low, a large current flow throughthe winding is made possible. This permits the attain ment of maximumpower and torque from the motor J. In addition, the current flow throughthe motor winding 60 is in phase with the voltage of the alternatingcurrent supply conductors L and L because of the series resonantcircuit. The voltage across the motor winding 60, however, leads thecurrent by substantially because of the inductance of the winding 60.

Energizing current is supplied the motor winding 6! from the transformersecondary winding 5| through the anode circuits of the triodes 81 and 58through the circuits previously traced. A condenser 99 is connected inparallel with the motor winding BI and is so chosen as to provide aparallel resonant circuit having a unity power factor. This parallelresonant circuit presents a relatively high external impedance and arelatively low local circuit impedance. The relatively high externalimpedance is approximately the .same as the impedance of the anodecircuits of the triodes B1 and B8, and accordingly, provides efiicientoperation. The relatively low internal circuit impedance approximatesthe actual resistance of the winding BI, and since this resistance isrelatively low, the impedance of the local circuit is also relativelylow.

' For the first half cycle of the alternating voltage produced acrossthe terminals of the transformer secondary winding 5|, the anode of thetriode 6'! is rendered positive with respect to the center tap 98, andduring the following half cycle the anode of the triode 68 is renderedpositive with respect to the center tap. Accordingly, the triodes 61 and68 are arranged to conduct on alternate half cycles of the alternatingcurrent supplied-,by the supply conductors L and 1..

When no signal is impressed upon the control electrodes of the triodes61 and B8, pulsating unidirectional current of twice the frequency ofthe alternating voltage supplied by conductors L and L is impressed onthe motor windin 5|. When .thus energized the motor J is not urged torotation in either direction but remains stationary. Due to therelatively high direct current component of the current then flowingthrough the motor winding 6| the core structure of the motor winding Jtends to become saturated whereby the inductive reactance to the motorwinding BI is made relatively small. The value of the condenser 99, inshunt to the motor winding Bi, is so chosen that the condenser and motorwinding then provide a parallel resonant circuit. This saturation of thecore structure of the motor J operates to exert an appreciable dampingeffect on the rotor 54, or in other words, an effect tending to preventrotation of the rotor 54. Consequently, if the rotor 54 has beenrotating, saturation of the motor core structure operates to quicklystop the rotation.

motor winding 6| during the first half cycle will 1 predominate overthose supplied the motor winding during the second half cycle. Whichanode current will be increased depends upon whether the bias voltage isin phase or 180 out of phase with the voltage of supply conductors L andU.

Such energization of the motor winding 61 operates to introduce thereinan alternating component of current of the same frequency as thatsupplied by the alternating current supply conductors L and L. Thisalternating component of current will either lead or lag the alternatingcurrent flowing through the motor winding 60 by approximately 90depending upon which of the triodes 61 and 68 has its anode currentincreased by the prevailing grid signal voltage, and with eitherphase-relation the two currents produce a magnetic field in the motorcore structure which rotates in one direction or the other, dependingupon said current phase relation, and effects rotation of the motorrotor 54 in the corresponding direction. Moreover, when the motorwinding 6| is so energized, the direct current component of the currentflowing therein is decreased, and consequently, the saturation of themotor core structure is decreased with the result that the rotor dampingeffect is reduced.

When the temperature of the thermocouple E is steady and the positionsof the pen carriage D and the contact C are correct for thattemperature, no signal potential is transmitted to the controllingelectrodes of the triodes 61 and 68 by the anode circuit of the triode65. Since the grid bias potential is then zero, the rotor 54 of themotor J has no tendency to rotate. Upon an increase in the temperatureof the thermocouple E, a signal potential-will be applied to the controlelectrodes of the triodes 61 and 68 by the anode circuit of the triode65 which will result in rotation of the motor J in a direction to movethe pen carriage D up-scale. Conversely, upon a decrease in thetemperature of the thermocouple E, a signal potential will be applied tothe control electrodes of the triodes 61 and 68 by the anode circuit ofthe triode 65 which will result in rotation of the motor J in adirection to give the pen carriage D a down-scale adjustment.

With the control winding 6! of the motor J connected to ground throughthe transformer winding 30 and condenser 32, as shown, the transformer24 couples the output and input circuits of the electronic amplifyingsystem. The coupling transformer is then operative to transfer energyfrom the output circuit to the input circuit of the system as requiredfor the maintenance of an oscillating current flow at a frequencydetermined by the parameters of the coupled circuits. The electronicamplifying and control system shown in Fig. 1 is of a standard and wellknown type, which has been in extensive use in this country for severalyears, and typical values of its resistance, inductance, and capacitanceelements, and of its energizing voltages. are well known.

For the purposes of the present invention, the precise frequency of thehigh frequency oscillation current maintained is not critical.Advantageously, however, it is' of the order of 15 to 30.

kilocycles, in which frequency range the amplifier gain is considerablylower than it is in its normal operating range .of 60 cycles.Consequently the high frequency oscillation does not overload theamplifier, nor significantly interfere with the availableamplifier'power output. To maintain current oscillations of thatfrequency in the standard amplifying system shown, the in ductance ofthe primary winding 30 may well be.

sistance 2| is employed to minimize the effect of; changes in resistanceof the potentiometer circuit between the point F and the contact C asthe latter is moved along the range of the slide wire resistance B. I

Fig. 2 is a simplified showing of the feed back and amplifier inputsfrom which it is readily apparent that there are three circuit branchesfor high frequency current flow connected in parallel to the secondarywinding 23 of the coupling transformer 24, namely: the branch includingthe clamping resistor 22, thermocouple E, and condenser 26; the branchincluding the condenser 26, slider contact C, bridge point F, condenser33, thermocouple E, and the measuring bridge circuit connecting saidcontact and point; and the circuit including thermocouple E, condenser33, conductor 48, vibrator switch 48, transformer primary windings H and42, and switch contact member G and G.

As Fig. 2 makes clearly apparent, the condenser 39 maintainsv a highfrequency current path of flow through the last mentioned circuit branchduring the standardizing operation in which the switch member G isdisconnected from the contact member G'. The circuit branch in-' cludingthe damping resistor 22 is of relatively high impedance which does notvary in operation, and proper operation could be maintained even if thevalue of resistance 22 were materially lower than ohms. The resistance2| is needed because the resistance of the measuring circuit between thecontact C and point P varies quite widely as. the contact C is adusted,and can be quite low when that contact is at one end of its range ofmovement.

With the standard amplifying and control system shown, the highfrequency oscillating current will ordinarily be maintained duringalternate half-cycles only of the 60 cycle alternating supply voltageused in energizing the power stage of the system. This is due to thefact that the phasing of the input transformer H changes during eachhalf cycle and one phase only.is suitable for generation of highfrequency signals. However, if an excessive amount of .feed back signalis supplied to the thermocouple input circuit, high frequencyoscillations are produced during each half cycle, probably as a resultof the capacitance coupling of the windings of the input transformer H.

The amplifying and control apparatus shown in Fig. 1, including thecoupling connection between the arnplifier input and output circuitshereinafter described, is so proportioned and arranged that in regularuse the high frequency signal may be detected in the amplifier outputcircuit at all times at which the 60 cycle signal impressed on theamplifier input circuit does not exceed its maximum normal operationvalue, and will disappear when the 60 cycle signal increases above saidvalue.

Any interruption of the high frequency current flow operates through thedetector circuit, shortly to be described, to open the switch H andthereby prevent further operation of the motor J until the groundconnection to the motor winding 0| is re-established.

With the apparatus shown in Fig. 1 in its normal operating condition,the high frequency signal is maintanied as well when the potentiometersystem is balanced and the motor J is stationary, as when the system isunbalanced and the motor J is revolving in one direction or the other atmaximum speed. Moreover the high frequency oscillating current will notbe interrupted by the adjustment of the switch member G, or as a resultof changes in the thermocouple electromotive force and the resultantrebalancing adjustments of the slider contact C. The high frequencycurrent will be interrupted, however, by the development of any one ofnumerous defects or failures in the amplifying and control system whichwill prevent the apparatus from functioning properly.

Thus the high frequency current flow will be interrupted not only on abreakage in the thermocouple, but also when an incipient thermocouplefailure results in a substantial increase in the thermocoupleresistance. Normally the resistance of the thermocouple is so small asto be negligible in this connection, but in an incipient stage of itsfailure the thermocouple resistance may increase to one or two hundredohms before the actual thermocouple breakage occurs. As Fig. 2 makesapparent, such an increase in thermocouple resistance would interruptthe high frequency current fiow through all of its paths of flow in theinput circuit portion of the amplifying and control system. The highfrequency current will also be interrupted on the failure of any of thevoltage amplifier tubes, and on the development of any defect in thecontrol system causing any one of the amplifier tubes to be over-driven.Furthermore, any mechanical failure of the motor preventing the latterfrom rotating will soon interrupt the high frequency current as theresult ant measuring circuit unbalance increases so that a 60 cyclevoltage signal will be impressed on the amplifier, which is large enoughto over-drive any one of the amplifier tubes.

The appearance and disappearance of the high frequency signal underdifferent conditions as above described may be explained as follows. Inthe contemplated use of the apparatus shown in Fig. 1, the highfrequency signal rides on top of the normal 60 cycle signal impressed onthe amplifying and control system through the transformer H, and iscontinuously apparent in the amplifier output circuit so long as theamplitude of the 60 cycle signal is within its normal predeterminedrange. The high frequency signal is clipped or interrupted as a resultof cut-off and/or saturation of the plate current in the third stageamplifying triode 05 on an abnormal increase in the 60 cycle signalproduced by the development Of any of the above mentioned operationdefects. The conditions of operation under which the high frequencysignal will and will not ride through the amplifier on the 60 cyclesignal, may be varied by changing the amplitude of either or both ofsaid signals. Inordinary practice, however, the apparatus must be soproportioned and arranged that the maximum normal amplitude of the 60cycle signal is that required to insure the desired operationcharacteristics of the rebalancing motor J. It is readily possible,however, i: make the amplitude of the high frequency signal such thatthat signal will be readily detectable in the amplifier output circuitat all times in which the 60 cycle signal is not abnormally high.

In this connection, assume that the apparatus is so proportioned andarranged that with intermediate values of the two signal currents, thehigh freqency signal will appear in the amplifier output circuitsuperimposed upon the peak portions of the low frequency signal current.

With apparatus so proportioned and arranged, the extent of increase inthe low frequency signal current required to prevent the appearance ofthe high frequency signal in the output circuit may be increased anddecreased by respectively increasing and decreasing the high frequencysignal current.

A detector circuit operative to open the switch IIS and if desired, toactuate a signal on the interruption of the high frequency current, maytake various forms. In Fig. l I have illustrated the detector circuitwhich I now consider preferable for use in an arrangement of the typeshown in Fig. 1. This detector circuit comprises electronic amplifyingand control means for amplifying the high frequency potential differencebetween the conductor 50 and ground. It also comprises anelectromagnetic relay mechanism controlled by said means and operatingthe previously mentioned switch H0, and, as shown, also operating asignal controlling switch H1.

The detector system of Fig. 1 comprises an electronic valve I00 havingits anode and its control electrode connected to the conductor 59through a branch conductor IM and a condenser I03, and having itscathode connected to ground through a resistance I02 which may be of twomegohms. To suitably minimize the amount of amplification of 60 cyclesignal reaching the valve I00, I provide a filter comprising a condenserI03 through which the conductor MI is connected to the anode of valveI00, and a resistance I 04 through which said anode is connected toground. The condenser I03 may have a capacitance of 2500micro-microfarads, and the resistance I04 may be 10,000 ohms. As shown,a condenser I05of 0.05 microfarad is connected in parallel with theresistance I02. The cathode of valve I00 is also connected through aresistance I06, which may well be 0.25 megohm, to the control grid of asecond electronic valve I01. The latter is a triode and may be thesecond of the two valves of 9. IN! tube, the valve I00 being the firstvalve.

The plate circuit of the valve I01 includes the secondary winding I08 ofa transformer I09 which has its primary winding IIO connected to the 60cycle supply conductors L and L One terminal of the secondary windingI08 is connected to the cathode of the valve I01 by a variableresistance III having a maximum resistance value which may well be 500ohms. By varying the amount of the resistance I I I in circuit, thesharpness of the response to the decrease in the high frequency signalmay be regulated. A secondary winding II! of the transformer I09 isemployed to raise the potential of the cathode of the valve I01 relativeto the ground potential and to the -mechanism which when energizedcloses the pre-- viously mentioned switch I I6 and opens the signalswitch I I1. As shown, a condenser I I of 8 microfarads capacity isconnected in shunt to the winding I. The switch II'I, when closed,connects the terminals of an alarm, which may be an electric lamp H8 oran electric bell, to the supply conductors L and L The switch H0 isbiased to open its contacts when the winding III is deenergized, and theswitch III is biased .to close its contacts when the winding Ill isdeenergized.

As those skilled in the art will recognize, the apparatus by which thehigh frequency feed back signal is introduced into the amplifying'andcontrol system may take various forms. In Fig. 3, I have illustrated aninput and output coupling arrangement quite different from that shown inFig. 1. Fig. 3also shows a modification of the detector system shown inFig. 1. The apparatus shown in Fig. 3 may be included in. apparatusexactly like that shown in Fig. 1, except for differences which areshown in Fig. 3.

\In Fig. 3, I make use of a coupling transformer 24A having secondaryand primary windings 23 and 30, respectively, and which may be like thetransformer 24 of Fig. 1 in all other respects, except that it does notrequire or include the adjustable core 29 of the transformer 24. Thesecondary winding 23 of the transformer 24A of Fig. 3 is connected inseries with the thermocouple E as in Fig. 1. The connections to theprimary winding 30 of Fig. 3 are quite different, however, from thoseshown in Fig. 1. In Fig. 3, one terminal of the winding 30 is connectedto a contact I adjustable along a potentiometer resistance I2I. Thelatter may be of 500 ohms,

and has one terminal connected to the second terminal of the winding 30and to ground. The second terminal of resistance I2I is connectedthrough a condenser I22 and a conductor I23 to the amplifying andcontrol system output conductor 59 which in the Fig. 3 arrangementconnects the motor winding 0|, not shown, to one terminal of a chokecoil I 24. As shown, the choke coil I24 has its second terminalconnected to the starting switch 3| and to the relay switch II8 just asdoes the corresponding terminal of the winding 30 in the arrangementshown in Fig. 1. In a practically operative embodiment of the form ofthe invention illustrated in Fig. 3,

the values of the condenser I22 and the choke coil I24 are 1000micro-microfarads and 30 millihenries respectively.

The detector circuit shown in Fig. 3 is in many respects like that shownin Fig. l, and corresponding detector circuit parts are designated bythe same reference symbols in both figures. In Fig. 3, the filteremployed to avoid 60 cycle voltage 'action on the detector includes asecond filter condenser I25 interposed between the resistance I 06 andthe junction between the condenser I02 and the ungrounded end of theresistance I04. The condenser I25 may be of 2500 micromicrofaradscapacity. In Fig. 3, the anode of the valve I 00 is connected to thecontrol electrode of that valve, and to ground. The cathode of the valveI00 is connected to the junction between the condenser I20 andtheresistance I 06 and to the control grid of the valve I01 through theresistance I00, as in Fig. 1. The condenser III of Fig. 1 is replaced inFig. 3 by a condenser I21 and a resistance I20 connected in series. Thecondenser I21 may have a capacity of .05 microfarad and the resistanceI20 may be a half megohm. Except as above noted, the detector circultand associated signal circuit of Fig. 3 are exactly like those of Fig.1, except that the variable resistance or rheostat III in the cathodecircuit of the valve I0I of Fig. 1 is omitted in Fig. 3.

There is no essential difference between the general operation of theapparatus shown in Fig. -1 and the same apparatus when modified, asshown in Fig. 3, only by the substitution of the input and outputcircuit coupling connections and detector circuit of the latter figure.The coupling of the detector circuit of Fig. 1 is simpler, however, thanthat shown in Fig. 3, and some of the impedance elements shown in Fig. 3are appreciably more costly to produce than the elements used in lieu ofthemin Fig. 1.

It is to be noted that the precise impedance and voltage valueshereinbefore stated, are not critical and all of them are subject tomodification as conditions make desirable. The values stated, however,are values which have been tested and found suitable for the purposeshereinbefore stated.

Heretofore potentiometric measuring and control apparatus of the generaltype illustrated herein has included safety provisions, different fromthos disclosed herein, for preventing improper operation of theapparatus as a result of some apparatus failure or failures. I believe,however, that I am the first to use the amplifier of such apparatus increating a high frequency oscillation current used in providingprotection against injurious operation resulting from apparatus failure.I also believe that no prior embodiment of potentiometric measuring andcontrol apparatus of the type illustrated has included means providingprotection against the injurious results of as many different forms ofapparatus failure as does the embodiment of my invention disclosedherein. I know of no prior arrangement including a measuring circuitnetwork and a rebalancing motor in which a motor defect preventingnormal motor operation will actuate an alarm signal device. I believe Iam the first, also, to provide measuring and control apparatus of thegeneral type disclosed, with protective means automatically actuated byan incipient thermocouple failure, when that failure is one which hasnot made the thermocouple circuit non-conductive, but has materiallyincreased the thermocouple resistance.

The means which I have devised for utilizing the amplifier of measuringand control apparatus of the general type disclosed herein, in creatinga high frequency oscillating current may be employed in arrangementsserving purposes other than the safety purposes described herein, and inmy copending application -Serial No. 678,256, filed concurrently withthe instant application, I

'have illustrated arrangements in which such a high frequencyoscillation current is utilized to produce a control effect when balanceis attained, or closely approached, at the end of a rebalancingoperation. The control effect thus produced may subject the rebalancingmotor to a damping action or it may actuate a recording mechanism. In

said copending application, I generically claim certain inventivefeatures disclosed in common in that application and in the instantapplication. There are illustrated in Figs. 4 to '1, inclusive, furtherembodiments of the present invention wherein are provided means forautomatically replacing various of the system components with equivalentstand-by components, should the original components become defective andinoperative. As was previously mentioned herein, in the automaticcontrol of numerous processes it is essential that the process be keptin operation continuously over a desired period, any interruption of theprocess during this period generally being costly and wasteful, andhence, highly undesirable. Therefore, upon failure of the automaticcontrol system controlling such a process, it is not desirable to havethe process halted by such failure, but it is desirable and practical insuch cases to provide automatic means for replacing with stand-bycomponents the particular component or components whose failure hasproduced the control system failure. Such means are provided in thesystems about to be described, the system of Fig. 4 being provided witha standby thermocouple, the system of Fig. 5 being provided with astand-by amplifier and motor drive circuit as well as a stand-bythermocouple, and the system of Fig. 6 being provided with a standbymeasuring circuit and a stand-by rebalancing motor in addition to thestand-by equipment of the system of Fig. 5. In Fig. 7 are illustratedmeans for shifting process control from the main portion of the systemof Fig. 6 to the stand-by portion when the latter is substituted for theformer upon failure of the main portion.

Specifically, there is illustrated in Fig. 4 an embodiment of thepresent invention wherein the high frequency oscillation signal derivedas previously described is utilized in a measuring system, similar tothat illustrated in Fig. i, to effect replacement of the thermocouple Eshould the latter fail and become open-circuited while the system is inoperation. As shown, the system of Fig. 4 comprises a measuring circuitI29 which consists of the potentiometric bridge circuit A, thethermocouple cold junction, the condensers 33 and 20, and theresistances 2i and 22 all as shown in Fig. 1. The system of Fig. 4 alsoincludes an amplifier and motor drive circuit I30 which comprises thefollowing components of Fig. 1: the converter I, the input transformerH, the feedback transformer 24, the power transformer I, the amplifiercircuit including the amplifying tubes M and L and associatedcomponents, and the motor drive circuit including the tube K andassociated components. The circuit I30 also includes a terminal I3Iwhich is connected to the reed 40 of the vibrator I, a terminal I32which is connected to the junction between the primary winding sectionsII and 42 of the input transformer H, terminals I33 and I'34 which areconnected to the lower ends of the secondary and primary windings 23 and30, respectively, of the feed-back transformer 24, terminals I35 and I35which are connected to the respective ends of the primary winding 50 ofthe power transformer I, and terminals I31 and I30 connected,respectively, to the upper end of the primary winding 30 of thetransformer 24 and to the center tap 90 on the secondary winding 5| ofthe transformer I. In Fig. 4, only certain components of the amplifierand motor drive circuit I30 just described are shown, in order not tounduly complicate the drawing. All components of the circuit I30, notshown in Fig. 4, are identical with, and

are connected in the same manner as the corresponding components of Fig.1.

The circuit of Fig. 4 also includes the following: a stepping switchgenerally designated at I39, a thermocouple E, electromagnetic relays Nand O, a time delay relay P, and a detector circuit I40, as well as thefollowing components as shown in the circuit of Fig. l: the motor J, themotor condensers 51 and 99, the supply conductors L and L thepush-button starting switch 3|, the thermocouple E, and the warning lampI1 8. The apparatus of Fig. 4 may comprise standardizing provisions asshown in Fig. 1, but no such provisions are shown in Fig. 4 in order toavoid unnecessary complication of the drawing.

The detector circuit I40 of Fig. 4 comprises the following components asshown in Fig. 1: the condensers I03, I05, and H5, the tubes I00 and I01,the resistances I02, I04, I05, and III, and the power transformer I09.These components are connected as shown in Fig. 1 to form a detector forthe high frequency oscillation signal substantially as describedhereinbefore. The circuit I40 also includes a terminal I4I which isconnected to the anode of the tube I00 through the condenser I03, aterminal I42 which is connected to the anode of the tube I00 through theresistance I04, terminals I43 and I44 connected. respectively, to theanode of the tube I01 and to the upper end of the secondary winding I08of the transformer I09, and terminals I45 and I45 connected,respectively, to the opposite ends of the primary winding IIO of thetransformer I09.

The stepping switch I39 comprises a plurality of relatively stationarycontacts of which the contacts I41 and I48 are examples, and a movablecontact member I49 adapted to successively engage said stationarycontacts and actuated through a ratchet wheel I50 and associated pawlmembers I5I and I52 from a plunger I53 operating in a coil I54. Theswitch I39 is so arranged that upon each energization of the coil I54,the plunger I53 and pawl member I5I will advance the movable contact armI49 from one stationary contact to the next, for example from thecontact I41 to the contact I49. The pawl I52 prevents motion of thecontact arm I49 in a reverse direction during the return motion of theplunger I53 which occurs when the coil I54 is de-energized. A brushmember I55 is in contact with the contact arm I49 to connect the latterto the external circuit.

The relay N comprises an operating coil NI, a pair of normally closedcontacts N2, and a second pair of normally closed contacts N3. Normallyclosed contacts are closed when their associated operating coil istie-energized. The relay 0 comprises an operating coil 0|, :1 pair ofnormally closed contacts 02, and a pair of normally open contacts 03.Normally open contacts are open when their associated operating coil isde-energized.

One terminal of each of the thermocuples E and E is connected by aconductor I55 to a terminal I51 of the measuring circuit I29, which inturn is connected to the slider contact C of the bridge circuit Athrough the thermocouple cold junction and the resistances 2i and 22.The bridge terminal F is connected by a conductor I58 to the inputterminal I3I of the amplifier and motor drive circuit I30. The terminalI33 of the latter circuit is connected by a conductor I59 to the movablecontact member I49 of the switch I39 through the brush I55. From thecontact arm I49, the conductor I59 is connected to whichever of thecontacts I41 and I48 and the associated thermocouples E and E that is incontact with the arm I49. It can thus be seen that either of thethermocouples E or E or any other thermocouples, not shown, which may beconnected to the other stationary contacts, will be connected into themeasuring and amplifying circuit in the same manner as shown in Fig. 1,with the difference, as herelnbefore mentioned, that no standardizingprovisions are shown in connection with the apparatus of Fig. 4.

The power winding 60 of the motor J is connected in series'withcondenser 51 across the supply conductors L and L The terminal 58 of thecontrol winding SI of the motor J is connected to the terminal I38 ofthe circuit I30 and. thence to the center tap 98 on the transformersecondary winding 5I. The other terminal 59' of the motor winding 0| isconnected to the terminal I31 of the circuit I30 and thence to the upperend of the primary winding 30 of the transformer 24. The condenser 99 isconnected in parallel with the motor control winding GI. The terminal50' is also connected by the conductor IOI to the input terminal I4I ofthe detector circuit I40. The energizin terminals I35 and I36 of thecircuit I30 are respectively connected by branch conductors I60 and I6Ito the supply conductors L and L. The connections to the motor J of Fig.4 are seen, therefore, to be the same as those of Fig. l.

The terminal I32 of the circuit I30 is connected to ground, as is theterminal I42 of the circuit I40. The coil NI of the relay N is connectedbetween the terminals I43 and I44 of the detector circuit I40, as is thecoil II4 of Fig. 1. The energizing terminals I45 and I46 of the circuitI40 are respectively connected by branch conductors I62 and I53 to thesupply conductors L and L.

The coil OI of the relay 0 is connected in series with the contacts N2between the con ductors L' and L One terminal of the coil I54 of theswitch I39 is connected by a conductor I64 and through the contacts N3to one output terminal of the time delay relay P. The other terminal-ofthe coil I54 is connected by a conductor I65 to the other outputterminal of the relay P, and the input terminals of the latter arerespectively connected to the conductors L' and L The time delay relay Pconnects the coil I54 and contacts N3 in series between the conductors Land L at a predetermined time after the line switch I85 located in theconductor L is closed, for a reason to be explained hereinafter.

The terminal I34 of the circuit I30 is connected to ground through therelay contacts 02 of the relay 0 and through the push-button switch 3|.Thus the terminal 59' 'of the motor control winding GI is groundedthrough the transformer primary winding 30 in a manner similar to thataccomplished by the switch IIB of Fig. 1. The warning lamp H8 isconnected in series with the contacts 03 of the relay 0 between theconductors L and L The relay 0 is of the time delay pick-up,instantaneous drop out type, but the time delay period of the relay 0 isquite shorter than that of the relay P, as will be ex plainedhereinafter.

In the operation of the apparatus of Fig. 4, on the assumption that theswitch I66 is open and that the apparatus is consequently deenergized,and also that the switch I39 is in the position shown, with contactmembers I41 and I49 in contact and thermocouple E connected in themeasuring circuit, the relays N and 0 will be de-energized, and thesignal lamp II8 will be extinguished. When switch I55 is closed, thetubes in the circuits I30 and I40 will start to heat up, and at first,no high frequency signal will be set up. Relay N, will therefore remainde-energized, energizing relay 0 which will pick up at the end of itstime delay period. Switch I39 will not as yet have its coil I54energized due to the time delay of the relay P. When relay O'picks up,the warning lamp I I8 will light, indicating that no high frequencysignal is present as yet. After the warm-up period has elapsed, duringwhich time the push-buttom switch 3I should be manually held in theclosed position, the high frequency signal will appear in the system,assuming that all is in order. At this point, the relay N will beenergized, which will de-energize the relay 0. This causes the warninglamp II8 to be extinguished, and causes the motor J to be permanentlyconnected in circuit, allowing the push-bottom switch 3| to be released.By this time, the relay P will have pick-up, but since the relay N isnow energized, the coil I54 of the switch I39 will remain de-energized.The apparatus will now operate normally, in the usual manner.

Upon a failure of some component or components which causes the highfrequency signal to disappear from the system, the relay N will bede-energized and the coil I54 will thereby be energized. The switch I39will operate, therefore, to disconnect the thermocouple E from themeasuring circuit and to connect in its place the second thermocouple E.In the meantime, the relay 0 will be energized, but will not pick-up dueto its time delay action. If failure or incipient failure of thethermocouple E was the cause of the disappearance of the high frequencysignal, the replacement of the thermocouple E by the thermocouple E willcause the high frequency signal to reappear and the relay N to bereenergized before the relay 0 has had sufiicient time to pick-up.Operation of the system will then continue as before the failureoccurred.

If failure of the thermocouple E was not the cause of the high frequencysignals disappearance, replacement of the thermocouple E by thethermocouple E will not produce a reappearance of the high frequencysignal. Consequently, the relay N will remain tie-energized, and therelay 0 will remain energized, and at the end of the time delay periodof the latter, the relay 0 will pick-up, de-energizing the motor J andcausing the warning lamp II8 to be lighted. The same operation as justdescribed will occur upon a second failure following a failure of thethermocouple E, If desired, additional thermocouples can be connectedbetween the conductor I56 and the stationary contact members of theswitch I39, providing further thermocouple failure stand-by protection.Upon the failure of the second thermocouple, therefore the third will betried, and upon failure of the third, the fourth will be connected tothe measuring circuit. and so on until all of the thermocouples havefailed, at which time the motor J will be de-energized and the warninglamp lighted. No matter how many thermocouples are provided, a failureother than that of a thermocouple will cause the warning lamp to belighted in the same time after the failure as described above, sincethis time is the time delay period of the relay 0. This time delay ismade just long enough to permit switching from one thermocouple to thenext. The time delay of the relay P is made sufliciently long so thatthe switch I30 cannot operate until the circuits I30 and Ill have hadsuflicient time to bring their tubes up to normal operating temperature.

In Fig. 5 is illustrated a modification of the apparatus of Fig. 4 whichprovides amplifier and motor drive circuit stand-by protection inaddition to thermocouple stand-by protection. The apparatus of Fig. 5comprises the thermocouples E and E, the measuring circuit I28, theamplifier and motor drive circuit I30, the motor J and associatedcondensers 51 and 30, the relay N, and the detector circuit I40. all asshown and described hereinbefore. In addition, the system of Fig. 5comprises a second amplifier and motor drive circuit I30 and a stand-bycontroller I01, the latter replacing the switch I30. the relays O and P,and the warning lamp H3. The circuit I30 may well be, and is shown asbeing identical with the previously described circuit I30, havingterminals I3I'. I32, I33, I34, I35, I36, I31, and I38. corresponding tothe similarly-numbered terminals oithe circuit I30. The internalconnections of the circuits I20, I30, I30, and I are identical in Fig.with the corresponding circuits of Figs. 1 and 4, hence these circuitsare shown in simplified form in Fig. 5 in order not to cause unnecessarycomplication of the drawing.

The stand-by controller I31 of Fig. 5 comprises a plurality oielectromagnetic and electrothermal relays Q. R, S, T, and U, therespective component parts of which are not shown in their usualphysical relation in order to avoid unnecessary complication of thedrawing. The represenation of the controller I31 is thereby made in Fig.5 by a so-called "across the line drawing, wherein the various contactsforming the different relays are not necessarily shown in their actualphysical relationship. Also, various of the relay contacts are shownphysically external to the controller circuit, but actually all of theserelay contacts are physically located within the controller proper.

The controller I61 al o includes a plurality of indicating lamps I80,I00, I10, HI. and I12, the function of which will be describedhereinafter.

The relay N is also preferably located within the controller proper.

The relay N comprises an operating coil NI, and 2 pairs of normallyclosed contacts N2 and N3. respectively. Relay N is of the instantaneouselectromagnetic type as in the circuit 01 Fig. 4. The relay Q is also ofthe instantaneous electromagnetic type comprising an operating coil QI.four pairs of normally open contacts Q2, Q3, Q. and Q3, respectively,and two pairs 01 normally closed contacts Q6 and Q1, respectively. Therelay R. which is shown in detail in Fig. 5A, is oi the electrothermal tme delay pick-up, lock-in type. comprising a heating coil RI, six pairsof normally open contacts R2, R3, R4, R5, R6, and R1, respectively, andfive pairs of normally closed contacts R3, R3, RIO, RI I, and RIZ,respectively. The relay R also comprises a bimetallic actuating memberRA which is in thermal contact with the heating coil RI. When the coilRI is energiaed, it produces heat. which causes bending movement of theactuating member RA to the lei t as viewed in Fig. 5A. This movement isoperative through a linkage RB to close the normally open contacts R2,R3, R4. R3, R8. and R1 and to open the normally closed contacts R3,

20 R3, RII, RII, and RII. This action is termed pick-up, and occursafter the time delay period has elapsed from the time the heating coilwas first energized. Once the contacts are in the positions Justdescribed, a relay latching mechanism RC locks the actuating member RAin the picked-up position, so that upon subsequent deenergization of theheating coil RI, the normally open relay contacts remain closed and thenormally closed contacts remain open, until the relay is manuallyunlatched or reset by an operator.

The latching mechanism RC includes an arm member RD which is pivotallysecured to the body of the relay at RE. The arm RD carries a bent latchportion RF which is held in engagement with the end of the actuatingmember RA by a spring RG, as shown in Fig. 5A. When the heating coil RIis energized and consequently heats up, causing the upper end of themember RA to bend to the left in Fig. 5A, the latch portion RF rides upon the end of member RA, allowing the latter to pass beneath the arm RD.Further bending of the member RA, at the expiration of the time delayperiod, causes the latch portion RF to drop into holding engagement withthe right-hand side of the member RA, whereby the latter is held in thepicked-up position, the normally open contacts are held closed, and thenormally closed contacts are held open. when the heating coil RI and themember RA have subsequently cooled, the member RA can be returned to thedeenergized position by depressing a reset button RH. This button ismounted on. the arm RD and is operative when depressed to raise thelatch portion RF out of engagement with the member RA to allow thelatter to return to its normal position under the action of its ownresiliency, thereby opening the normally open contacts and closing thenormally closed contacts.

The relays S and T, about to be described, are also of this sameelectrothermal, time delay pickup, lock-in type. These relays have notbeen shown in detail since they are identical to the relay R, justdescribed, except as to the number of contacts operated thereby.

'Ihe'relay S comprises a heating coil SI and two pairs of normally opencontacts S2 and S3, respectively. The relay T comprises a heating coilTI, a pair of normally open contacts T2, and two pairs of normallyclosed contacts T3 and T4. respectively, The relay U is of the timedelay pick-up, electromagnetic type, comprising an operating coil UI anda pair of normally open contacts U1. The relay U has instantaneous dropout, and may well be like the relay P oi Fig. 4.

Also included in the controller I81 are an onoii' switch I13 and aresistance I14, the function of which will be described hereinafter. Itis to be noted in connection with the description of the relays Justgiven that the phrases normally open contacts" and normally closedcontacts refer to the condition in which the particular relay is notpicked-up, or in the case of an instantaneous relay, is not energized.This applies even though in operation, the particular relay may normallybe picked-up or energized.

In Fig. 5, one terminal of the thermocouple E is connected through thecontacts Q1 and by the conductor I56 to the input terminal I51 of themeasuring circuit I28. One terminal of the thermocouple E is alsoconnected to the conductor I36 through the contacts Q5. The remainingterminals of the thermocouples E and E are 21 connected together and .tothe terminal I33 of the amplifier and motor drive circuit I30 throughthe contacts RI I and'by the conductor I". These last mentionedthermocouple terminals are also connected through the contacts R and bya conductor III to the terminal I33 oi the circuit I30. The terminal Fof the circuit I20 is connected through the contacts RI. and by theconductor I50 to the terminal I3I of the circuit I30. and the terminal1'' is also connected through the contacts R and by a conductor III tothe terminal III of the circuit I 30'. The terminals I32, I34, I32, andI34 of the circuits I30 and I30 are all connected to ground.

The terminal 50 of the control winding II of the motor J is connected tothe terminals I30 and I30 of the circuits I30 and I30 respectively. Themotor terminal 53 is connected through the contacts RI2 and, by aconductor I to the terminal I31 of the circuit I30, and the terminal 53'is also connected through the contacts R1 and by a conductor I15 to theterminal I31 of the circuit I. The condenser 00 is connected between themotor terminals 50 and 53' as before.

The motor terminal 53' is also connected by the conductor IOI to theinput terminal I4I of the detector circuit I40. The terminal I42 of thelatter circuit is connected to ground. The relay coil NI is connectedacross the output terminals I43 and I44 of the circuit I as before.

In the controller I01, the relay coil UI is connected in series with theswitch I13 across the conductors L and L. The junction between theswitch I13 and the coil UI is connected through the contacts T4 and by aconductor I10, partially shown, to the energizing terminal I35 of thecircuit I30. The other energizing terminal I30 is connected by aconductor I11, partially shown, to the conductor L". The motor powerwinding 00, in series with the condenser 51, is also connected acrosstheconductors I10 and I11, and the energizing terminals I and I40 of thecircuit I40 are respectively connected to the conductors I10 and I11.

The conductor I10 is connected through the contacts R2 to a conductorI10, partially shown, which in turn is connected to the energizingterminal I35 of the circuit I30. The conductor I10 is also connected tothe conductor I15 through the resistance I14 and the contacts Q2,connected in series. The other energizing terminal I30 of the circuitI30 is connected by a conductor I13, partially shown, to the supplyconductor L. Y

A conductor I30 is connected to the conductor L through the contacts U2.Between'the conductor I30 and the conductor 1? are connected thefollowing: the contacts Q4 in series with the indicating lamp I12, thecontacts Q0 in series with the lamp "I, the contacts R4 in series withthe lamp I10, the contacts R0 in series with the lamp I03, and thecontacts T2 in series with the warning lamp I50.

A conductor III is connected to the conductor I00 through the contactsT3, and a conductor I32 is connected to the conductor I8l through thecontacts N3. Between the conductor I32 and the conductor L are connectedthe following: the relay coil RI, the relay coil SI in series with thecontacts R3, and the relay coil TI in series with the contacts 82.

One terminal of the relay coil QI is connected to the conductor IOIthrough the contacts N2. The other terminal of the coil QI is connectedto the conductor L through the contacts R0. The

22 contacts Q3 are connected in parallel with the tacts N2, and thecontacts 83 are connected in parallel with the contacts R3.

In the operation of the system of Fig. 5, onthe assumption that the lineswitch I00 is closed and that all is in order, but that the on-oifswitch I13 is open and the system is therefore inoper+ ative, all relaycontacts are in their normal positions as shown in Fig. 5, since all ofthe relay coils are de-energized and all relays are droppedout. When theswitch I13 is closed, the relay coil UI and the amplifier and motordrive circuit I 30 will be energized, as will be the detector circuitI40 and the power winding 00 of the motor J. As soon as the tubes of thecircuits I30 and I40 have come up to their operating temperatures, thehigh frequency signal will appear in the system, and the relay coil NIwill be energized, opening the contacts N2 and N3. By this time, therelay U will pick-up, closing the contacts U2, since its time delayperiod is adjusted to allow time for the various tubes to come to theiroperating temperatures. When the contacts U2 close, the conductor I00will be energized, and the lamps HI and I63 will be lighted throughcontacts Q0 and R0, respectively. The lamp "I may well be labeled"Thermocouple I" and the lamp I 03 may be labeled Amplifier 1." Thus'the lighting of the lamps HI and I09 will indicate that the system isemploying a certain thermocouple and a certain amplifier, these beingthe thermocouple E and the circuit I30 of Fig. 5. In this operatingcondition, which for convenience will be called condition 1, thethermocouple circuit can be traced from one terminal of the thermocoupleE and through the contacts Q1, the conductor I 50, the circuit I29, thecontacts RIO, and the conductor I53 to the input terminal I3I of thecircuit I30, through the circuit I30, not shown in Fig. 5, to theterminal I33, and through the conductor I53 and the contacts RII to theother terminal of the thermocouple E. The output circuit can be tracedfrom the output terminal I31 of the circuit I30, through the conductorI15 and the contacts RI2 to the motor terminal 59', through the motorcontrol winding GI to the terminal 53, and from there to the otheroutput terminal I33 of the circuit I30. The input to the detectorcircuit I40 is permanently connected between the motor terminal 59 andground by the conductor IOI and the grounded conductor as shown. Sincethe relay N is energized, the relays Q, R, S, and T will not beenergized.

When a failure occurs in the system of Fig. 5, the controller I51 willimmediately switch the system to operating condition 2, and upon asubsequent failure, or if condition 2 does not remedy the first failure,the system will be switched to operating condition 3. If condition 3does not remedy the failure, or upon a subsequent failure, the systemwill be switched to operating condition 4. If condition 4 does notremedy the failure, or if a subsequent failure occurs, the system willbe switched to alarm condition 5, wherein an alarm will be given and thesystem will be de-energized. For convenience, the major components whichwill be operatively connected in the system for the various operatingconditions are listed below:

Operating condition 1: thermocouple E and circuit I30.

Operating condition 2: thermocouple E and circuit I30.

Operating condition 3: thermocouple E and circuit I30.

Operating condition 4: thermocouple E and circuit I30.

When a failure occurs while the system is in condition 1, or if there isa system defect when the system is first put Into operation, the relay Nwill either be de-energized or will not have been energized at thestart, since there will be no high frequency signal present in thesystem. In either case, contacts N2 and N3 will be closed. which willenergize and pick-up relay Q, energize relay R, and place the system incondition 2. When relay Q picks up, it will seal itself in throughcontacts Q3 and will cause the lamp III to be extinguished by openingcontact Q0, the lamp I12 to be lighted through contacts Q4, the secondamplifier and motor drive circuit I30 to be energized with voltagesomewhat below line voltage through the resistance Ill and the contactsQ2 to allow the circuit I30 to be brought nearly to its operatingtemperature, and the thermocouple E' to be substituted for thethermocouple E in the thermocouple circuit by the opening of contacts Q1and closing of contacts Q0. The lamp I12 may well be labeled"Thermocouple II.

If the failure was due to the thermocouple E,

replacement of the latter by the thermocouple E will cause thereappearance of the high frequency signal and the relay N will beenergized the circuit I23, the contacts RIO and the conductor I08 to theterminal I3I, through the circuit I30 to the terminal I33, and throughthe conductor I53 and the contacts RII to the other terminal of thethermocouple E. The output circuit for condition 2 is identical withthat of condition 1.

If the failure was due to something other than failure of thethermocouple E, substitution of the thermocouple E will not cause theappearance of the high frequency signal, hence the relay N will remainde-energized and the relay R will pick-up at the end of its time delayperiod and lock in. This places the system in condition 3, with thefollowing results: the second amplifier and motor drive circuit I30 willbe energized at full voltage through contacts R2, the relay coil Si willbe energized through contacts R3, the lamp I'I0 will be lighted throughcontacts R4, and the circuit I30 will be connected to the measuringcircuit I29 through R5, to the thermocouple circuit through R6, and tothe motor J through Rl. Also, the lamp I69 will be extinguished by theopening of contacts R8, the relay Q will be deenergized by the openingof contacts R3, and the circuit I30 will be disconnected from thecircuit I23, from the thermocouple circuit, and from the motor J by therespective opening of the contacts RIO, RI I, and RI2. De-energizationof the relay Q will remove the shunted resistance I" from the circuit bythe opening of contacts Q2, will extinguish the lamp in by the openingof contacts Q4, will disconnect the thermocouple E from the circuit I29by the opening of the contacts Q5, will light the lamp III throughcontacts Q3, and will connect the thermocouple E to the circuit I23through contacts Q1.

From the foregoing description it can be seen that in condition 3, thethermocouple E is again placed in use, the substitute thermocouple E isremoved from the circuit, and that the first amplificr and motor drivecircuit I30 is removed from the system and is replaced by the secondamplifier and motor drive circuit I30.

If the failure was due to the circuit I30, replacement of the latter bythe circuit I30 will cause the reappearance of the high frequencysignal, and the relay N will be energized and contacts N3 opened beforethe relay S has had suiilcient time to pick up. The relay coils willthen be de-energizcd, and since relay Q is not energized and relay R islocked in the picked-up position, the lamps III and I" will remainlighted. The lamp "0 may well be labeled Amplifler II.

The thermocouple circuit for condition 3 can be traced from one terminalof the thermocouple E-and through the contacts QI, conductor I56,circuit I23, contacts R5, and conductor I58 to the terminal I3I of thecircuit I30, through this circuit to the terminal I33, and through theconductor I53 and contacts R6 to the other terminal of the thermocoupleE. The output circuit for condition 3 can be traced from the terminalI31 of the clrcuit I30, through the conductor I15 and the contacts R1 tothe motor terminal 59, through the motor control winding 6| to theterminal 58, and from there to the other output terminal I33 of thecircuit I30.

If the failure was due to something other than the circuit I30, or wasdue to both the circuit I30 and the thermocouple E, substitution of thecircuit I30 will not cause the high frequency signal to appear, hencethe relay N will remain deenergized and the relay S will pick up at theend of its time delay period and lock in. This places the system incondition 4, with the following results: the relay coil TI will beenergized through contacts S2, and the relay coil QI will be energizedthrough contacts S3. Therefore, the relay Q will pick up and be sealedin by the contacts Q3, the lamp I12 will be lighted through contacts Ql,the thermocouple E will be connected in the system through contacts Q5,the lamp III will be extinguished by the opening of contacts Q5, and thethermocouple E will be removed from the circuit by the opening ofcontacts Q1.

From the foregoing description it can be seen that in condition 4, thethermocouple E is again replaced in the system by the thermocouple E,and that the latter is connected to the input of the second amplifierand motor drive circuit I30.

If the last mentioned failure was due to the thermocouple E, replacementof the latter by the thermocouple E will cause the appearance of thehigh frequency signal, and the relay N will be energized and contacts N3opened before the relay T has had sufficient time to pick up. The relaycoil TI will then be de-energized, and since relays R and S are lockedin, and relay Q is sealed in, lamps I12 and I10 will remain lighted.

The thermocouple circuit for condition 4 can be traced from one terminalof the thermocouple E and through the contacts Q5, conductor I56,circuit I20, contacts R5. and conductor I50 to the terminal Ill, throughthe circuit I30 to the terminal I33, and through the conductor I59 andcontacts R3 to the other terminal of the thermocouple E. The outputcircuit for condition 4 is identical with that for condition 3.

